I agree that it's sad and frustrating to see stuff like this - but it's not a design goal.
I think you might be reading something into this that isn't there, or otherwise glossing over an important distinction. The frustration here is not (and should not be) directed toward the engineers and visionaries who designed the hardware and software. Yamaha's software and hardware design departments are world-class, even when accounting for foibles like the Montage MIDI implementation. That's why we're all here having this conversation in the first place.
The problems come from an entirely different wing of the company. This wing is filled with people who bring no value to the world aside from maximizing Yamaha's profit to the greatest degree that is legally and realistically possible. Unfortunately, the law provides for an avenue in which Yamaha's profits are able to grow significantly at the expense of product longevity. It's thanks to that part of the company that firmware updates and drivers are locked-down and eventually left to rot.
I can't imagine that the brilliant people who poured their blood, sweat, and tears into these products would ever want to see anything other than for those products to do as much as they possibly can for as long as they possibly can.
Unfortunately, unlike those designers, the individuals with the most influence over the company at the end of the day are not interested in the creation of musical instruments which are truly as high-quality and long-lasting as possible. As it stands, that is not the avenue toward maximizing profit.
Due to business culture and legal climate, it is more profitable for Yamaha-at-large to stifle the long-term growth of their products. This is done through a combination of withdrawing support (understandable) and throwing away the keys (unconscionable). This is all logical, predictable, and business as usual, given the state of legislation which all of us living in democracies have collectively made ourselves comfortable with: to the extent that we're comfortable saying things like "It's just the way it goes."
So, to say that it is "obsolescence by design" would be incorrect if we are speaking of Yamaha's engineering department. But it's entirely fair to say when speaking about Yamaha in general, because the engineering department is a very small part of that picture. Just as an intentional omission of the truth can be fairly described as a lie, neglect in combination with obstruction can be described as planned obsolescence.
The sad truth is that, because this is a problem with what businesses are legally allowed to do when it comes to locking-down their software and hardware (as well as what individuals aren't allowed to do in regards to removing those locks-- see: the DMCA, 17 U.S.C. 1201), there is really nowhere else to go for musicians. The same problems will be found at Roland, as well as at Korg, as well as at Kurzweil, and anywhere else you might care to take your money. And it remains the case that Yamaha makes the best products, despite their effective artificial expiration dates.
Perhaps the best thing we can do as customers of professional audio equipment, aside from relevant action as citizens of the democracies which allow businesses to operate in this way, is to entirely
abandon the workstation market. When you take a dozen excellent products and tie them together inseparably in a single box, as long as the reality of business remains such as it is, we all stand to lose more from obsolescence at the end of the day.